Patent Application
20120090596
This invention relates to direct vent, sealed combustion gas fireplaces. In particular, this invention is directed to a method and apparatus for controlling the air flow to enhance the operating efficiency of a direct vent, sealed combustion gas fireplace while accommodating the need for a relatively unrestricted air supply during ignition in a fireplace.
Unlike open flue wood or gas fireplaces that draw combustion air from the room in which they are located, the fireboxes of direct vent gas fireplaces are sealed from the room air. The fireplaces draw combustion air into the firebox from outside the building through air intake ducts and exhaust the combustion gases from the firebox out of the building through exhaust ducts. Air flow through the firebox and the ducting systems during operation of direct vent gas fireplaces is typically driven by thermal convection and the buoyancy of the combustion products. Relatively cool combustion air is drawn in and down a vertically offset run of inlet duct while heated air rises along a vertically offset run of the exhaust duct. Ideally, the intake and exhaust ducts are entirely vertical, but they may vent horizontally from a wall of the building provided there is an adequate vertical run to ensure gravity-fed operation.
As discussed in U.S. Pat. No. 5,267,552 to Squires et. al, air flow through the firebox and the duct system may be enhanced by a blower. This can be particularly useful when the ducts are not sufficiently vertical to rely on convection and the buoyancy of the gas combustion products.
One problem in the management of air flow of direct vent gas fireplaces is to ensure that a sufficient amount of combustion air is available during ignition of the fireplace while avoiding inefficiencies due to the loss of heated combustion products during operation of the fireplace. Optimizing the efficient operation of the fireplace entails restricting the excess air flow through the firebox and to the combustion gas outlet while the fireplace is in operation. However, such restriction poses a corresponding problem during start-up when the air in the intake and exhaust vents is cool and stagnant. In order achieve effective ignition of the burners, the air flow must be as unrestricted as possible so as to enable it to immediately begin moving. The failure to do so may result in lift-off of the flame and the ignition of pockets of built up gas, or in starving the ignition system of combustion air and a failure to maintain ignition.
The optimal air flow required for successful ignition is therefore greater than the air flow desired for maximum efficiency during operation of the fireplace. This trade off is usually addressed by, at the time of installation, selecting a degree of restriction for the fireplace that achieves a measure of efficiency during fireplace operation but that also provides for sufficiently unrestricted movement of air during start up. The solution is nonetheless inefficient.
European Patent App. No. 0268407 to Shimek et al. discloses a direct vent gas fireplace in which a primary air supply is provided through a primary air duct. However, when the combustion chamber is cold, there is not a sufficient supply of hot exhaust gases to produce or induce a draw from the primary air duct. A secondary slot is therefore provided to allow entry of a supply of secondary air directly to the burner area to assist in igniting the burner under cold conditions. This secondary slot is closed off by a pivoting damper, actuated by a bi-metallic element, once the fireplace has heated up sufficiently. While this approach may assist in maintaining ignition, it still suffers the drawback of significant heat losses during continued operation of the fireplace because it is not intended to control overall air flow through the fireplace.
In sealed combustion gas fireplace systems, the problem of ignition air volume is sometimes addressed by maintaining a standing pilot flame that generates a small amount of air flow through the fire box and venting system. This is particularly so in colder climates. However in some jurisdictions, the use of a standing pilot flame is falling out of favour with regulatory authorities because of perceived energy conservation reasons. As the standing pilot has almost universally been used to ensure air flow through the firebox and duct system in colder climates, the absence of a standing pilot creates a challenge to reliable ignition of the burner.
U.S. Pat. No. 5,503,550 to DePalma discloses a gas fireplace system in which a manually operated pilot light unit replaces the standing pilot light. An automatic damper mechanism, including a rotatable damper vane and a controller actuated by a motor, controls air flow through the flue in the fireplace. The controller is hard-wired into the electric lines of the building in which it is installed, which may make the system difficult to install or retrofit. In an alternative embodiment, the damper vane includes thermally-activated bi-metallic quadrants. However, the quadrants are designed to keep the flue closed until the fireplace produces enough heat that the vanes to flex to an open flue position. This does not assist in ensuring that there is a sufficient air supply at ignition of the fireplace burners.
U.S. Pat. No. 7,451,759 to Weiss et al. discloses a wireless damper control device for a fireplace, eliminating the need to hard-wire a control system into the building. This damper control system will open the damper immediately upon request to ignite the gas fireplace. Once the damper indicates to the control system that it is open, gas is allowed to flow to the ignition system. This should allow enough air to flow to successfully ignite the fireplace, but the circuitry and signalling required in this system is relatively complex. Further, in this system, the damper remains open during the burner operation and is only intended to close the flue system in the off cycle.
It is therefore an object of the present invention to provide for the efficient control of air flow in a direct vent sealed combustion gas fireplace that does not have a standing pilot, that maximizes the operating efficiency, while enabling sufficient air flow during a cold start to maximize the chances of successful ignition without the need for complicated electronics or signalling mechanisms.
This and other objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows. Note that not all of the objects are necessarily met by all embodiments of the invention described below or by the invention defined by each of the claims.
In one aspect, the invention comprises a method and apparatus to control the air flow into a direct vent sealed fireplace, in which the air flow through the firebox is minimized when the fireplace is cold, namely at initial ignition. The air flow is then restricted as the temperature increases. This arrangement provides sufficient air flow at ignition to prevent starvation of the ignition system, but minimizes the loss of heated air once the firebox is in full operation.
According to the invention, the air flow through the firebox is restricted as the temperature in the firebox or of the combustion gases increases. This may be accomplished automatically by means of a temperature sensitive deformable bi-metallic element. When the fireplace is cold, the air flow is unrestricted by the by-metallic element, allowing a relatively large volume of air from the air supply and venting system to quickly be displaced to support continued ignition, until the burner reaches normal operation, at which time operating efficiency is maintained by temperature sensitive restriction of the combustion air flow.
In the preferred embodiment, the air flow is restricted by means of a restrictor element that moves to at least partially obstruct an air flow passageway, preferably an air inlet into the firebox, the element being mechanically actuated by deformation of the bi-metallic element.
In one aspect, the invention comprises a direct vent gas fireplace having a sealed combustion system in which a combustion air supply and venting system is substantially sealed in relation to a room in which the gas fireplace is disposed, wherein the combustion air supply and venting system defines a passageway for combustion air and combustion products, and wherein the passageway is restricted in response to an increase in temperature. In a further aspect, the passageway may include a combustion air intake for drawing outside air into a firebox of the gas fireplace, and the combustion air intake may be restricted in response to an increase in temperature. In a further aspect, the passageway may include a combustion products exhaust for venting combustion products from a firebox of the gas fireplace to the outside, and the exhaust may be restricted in response to an increase in temperature. In yet a further aspect, the passageway may be restricted in response to an increase in temperature in a firebox of the gas fireplace, and/or in response to an increase in temperature in air flowing through the room. In yet a further aspect, the passageway may include a combustion products exhaust for venting combustion products from a firebox of the gas fireplace to the outside and the passageway is restricted in response to an increase in temperature in the exhaust.
In another aspect, the invention comprises a gas fireplace having a sealed combustion system in which a combustion air supply and venting system is substantially sealed in relation to a room in which the gas fireplace is disposed, the combustion air supply and venting system defining a passageway for combustion air and combustion products, and comprising a restrictor element operative to restrict the passageway in response to an increase in temperature. In a further aspect, the passageway may include a combustion air intake for drawing outside air into a firebox of the gas fireplace, and the restrictor element may be operative to restrict the combustion air intake. In yet a further aspect, the passageway may include a combustion products exhaust for venting combustion products from a firebox of the gas fireplace to the outside, and the restrictor element may be operative to restrict the exhaust. In a further aspect, the restrictor element may be operative to restrict the passageway in response to an increase in temperature in a firebox of the gas fireplace, and/or in response to an increase in temperature in air flowing through the room. In a further aspect, the passageway may include a combustion products exhaust for venting combustion products from a firebox of the gas fireplace to the outside, and restrictor element may be responsive to restrict the passageway in response to an increase in temperature in the exhaust.
In another aspect, the invention comprises a direct vent, sealed combustion gas fireplace comprising a firebox; an air intake for drawing combustion air into the firebox; an exhaust outlet for exhausting combustion products from the firebox; and a damper effective to restrict air flow through the firebox in response to an increase in temperature. The damper may comprise a bi-metallic element deformable under the influence of a change in temperature, and may further comprise a restrictor element actuated by deformation of the bi-metallic element. The damper may further comprise a shaft between the bi-metallic element and the restrictor element, the shaft actuating movement of the restrictor element along the shaft when the bi-metallic element deforms under the influence of a change in temperature. The bi-metallic element may comprise a pair of bi-metallic strips. In a further aspect, the bi-metallic element may be mounted in an enclosure on a wall of the firebox. In yet a further aspect, the restrictor element may be spring-biased toward a position wherein the restrictor element does not restrict the air flow when the firebox is cold. The restrictor element may be spring-biased against displacement in one direction. In yet a further aspect, the restrictor element may comprise at least one aperture.
In another aspect, the damper may operate in response to a change in temperature in the firebox, in the exhaust outlet, and/or in the air flowing from a room in which the fireplace is disposed.
In another aspect, the invention comprises a damper mechanism for a direct vent sealed combustion gas fireplace comprising a damper effective to restrict air flow through a firebox of the gas fireplace in response to an increase in temperature, comprising a bi-metallic element deformable under the influence of a change in temperature and a restrictor element actuated by deformation of the bi-metallic element. The restrictor element may be spring-biased against displacement in one direction. The bi-metallic element may comprise a pair of facing bi-metallic strips. The restrictor element may comprise a plurality of apertures. The damper may further comprise a shaft between the bi-metallic element and the restrictor element that actuates movement of the restrictor element along the shaft when the bi-metallic element deforms under the influence of a change in temperature.
In another aspect, the invention comprises a method of controlling combustion air flow in a direct vent, sealed combustion gas fireplace comprising the steps of providing a bi-metallic element positioned near an air passageway between the fireplace and a source of combustion air; restricting the air passageway by deformation of the bi-metallic element in response to an increase in temperature. In a further aspect, the deformation of the bi-metallic element may cause a restrictor element to move to restrict the air passageway. The bi-metallic element may be spring-biased away from the air passageway. In another aspect, the method may include the step of igniting a combustion gas source within a firebox in the fireplace to increase the temperature of the fireplace.
In another aspect, the invention comprises a damper mechanism for a direct vent sealed combustion gas fireplace, comprising a bi-metallic element responsive to temperature changes within the fireplace; and a biasing mechanism to bias the bi-metallic element away from an air passageway within the fireplace; wherein movement of the bi-metallic element in response to a temperature increase causes restriction of the air passageway by overcoming the bias. The biasing mechanism may comprise a spring. In a further aspect, movement of the bi-metallic element may actuate a restrictor element to move towards the air vent. The bi-metallic element may comprise a pair of bi-metallic strips. The restrictor element may further comprise a plurality of aperture.
The foregoing was intended as a broad summary only and of only some of the aspects of the invention. It was not intended to define the limits or requirements of the invention. Other aspects of the invention will be appreciated by reference to the detailed description of the preferred embodiment and to the claims.
The invention will be described by reference to the detailed description of the preferred embodiment and to the drawings thereof in which:
Referring to
Combustion air is supplied to the fireplace by means of an air inlet 18 and gas combustion products are vented through exhaust outlet 20. As best seen in
The air supply and venting system 60 is substantially sealed relative to the room in which the fireplace is located such that air flows only in from outside the building, through the firebox 14 and back outside though a vent terminal 62. When the fireplace is off, the air pressure inside the firebox 14 should equal the outside atmospheric pressure in the vicinity of the vent terminal 62.
Referring again to
In
The flow of air and gasses is also shown in
The components of the damper mechanism 22 of the preferred embodiment are shown in
The top surface of the uppermost bi-metallic strip 36a is in contact with shaft 38. A spring 40 is provided on shaft 38 and rests against a disk-shaped restrictor plate 42 through which shaft 38 extends. Bracket 46 is mounted across the air inlet 18 to retain the free end of shaft 38.
Restrictor plate 42 corresponds in diameter to the air inlet 18. Spring 40 biases restrictor plate 42 towards the bi-metallic strips 36, such that movement of bi-metallic strips 36 must overcome the spring force of spring 40 to move restrictor plate 42 which is therefore in a normally open state in relation to air inlet 18.
Restrictor plate 42 may be provided with one or more apertures 44, in order to allow some air flow into the fireplace insert, even when the damper mechanism 22 is in a closed position. The number and size of apertures 44 may be selected based on the minimum amount of air flow necessary for efficient operation of the fireplace.
The operation of damper mechanism 22 is shown in
Once the ignition has taken place and the burner is operating normally, a lower level of air flow is required for optimal operation of the fireplace. Bi-metallic strips 36, exposed to the heat generated within the firebox will flex under the heat, eventually reaching an active or closed vent position, best shown in
As it is not desirable to completely cut off the air flow to the fireplace, apertures 44 may be provided to allow some minimum constant air flow. Alternatively or in addition, the damper mechanism 22 may be adjusted, such as by lengthening the spring 40 or adjusting the position of the restrictor plate 42 on shaft 38, such that the restrictor plate does not contact the bracket 46. This embodiment would also restrict the air flow through the air vent 18 without closing off the vent completely.
The pair of bi-metallic strips 36 may be replaced with a single bi-metallic strip. It may be necessary to make appropriate adjustments, such as changing the length of the shaft 38 or the length of the spring 40 to ensure that the amount of flexion of the strip under typical heating conditions is sufficient to move the restrictor plate as far towards the air vent as necessary. The length of shaft 38 and the position of the restrictor plate 42 on shaft 38 may also be adjusted such that shaft 38 and bi-metallic element 36a are not in physical contact until after the bi-metallic element 36a has flexed a certain amount. After contact is made, the damper mechanism 22 will operate as described above, until the restrictor element 42 reaches its final position near air vent 18.
In an alternative embodiment, the restrictor element itself be a bi-metallic element, such that it flexes to directly restrict the passageway in which it is installed. Such an arrangement would reduce the need for multiple components in the damper mechanism but may require a lateral positioning of the restrictor along a portion of the passageway.
In the preferred embodiment, the damper mechanism is mounted on a firebox wall such that the bimetallic elements react to the changes in temperature in the firebox. Nonetheless, it is contemplated that the damper mechanism may be arranged in the combustion products exhaust system 58 (either in the exhaust duct 54 or in the vicinity of the exhaust outlet 20) to react to the increase in temperature of the combustion gases in that system as the fireplace enters full burning operation. Accordingly, the damper may be configured to react to changes of temperature in the combustion products exhaust system 58 rather than directly sensing temperature changes in the firebox 14. Alternatively, the damper mechanism 22 may be placed within convection passageway 32, from where it can respond to changes in temperature of the air flowing through convection passageway 32 to and from the room where the fireplace is located, in the same manner as described above.
It will be appreciated by those skilled in the art that the preferred and alternative embodiments have been described in some detail but that certain modifications may be practiced without departing from the principles of the invention.
